The Nokkers are the main "antagonists" of To Your Eternity, which is clear by how they seem content to just cause general mayhem and misery for humanity and Fushi. Of course, there's more to these creatures that Fushi doesn't know or has only been revealed in the manga and not the anime quite yet.
That said, there's a lot that To Your Eternity fans should know about the Nokkers that they may have missed in this fantastic show or maybe just didn't pick up on previously. So, let's go over some lesser-known facts about these weird orb-shaped antagonists that make this series (and other anime like it) so unique.
7 They Can Camouflage Themselves
First and foremost, viewers keep forgetting that Nokkers can actively disguise themselves by changing shape. They seem to take on forms based on their surroundings, such as becoming leaves or sticks in a forest or rocks and random debris in the Jananda terrain.
In the anime, this isn't seen all too often after Fushi fights them in the forest the first time with Pioran, as they start just burrowing underground to surprise from below after this, as seen especially at the start of season 2. It's not clear how extensive this disguise ability is, but it's clear that they can't replicate the human form in any realistic sense, as they just end up looking like people made out of wood when they try.
6 They're The Ultimate Adaptive Lifeforms
Whereas Fushi learns, grows, and changes constantly over time through adversity, new experiences, and even the deaths of those around him, the Nokkers change in a much less human and more mechanical way. Basically, they change by reacting and adapting to whatever hindered their last encounter. When Fushi first kills a Nokker by burning them with fire, they take on the appearance of a stone Oniguma the next time he encounters them to counteract this tactic.
When Fushi gets skilled enough to consistently break their stone or wooden shells using his weird powers, they start hiding in humans since Fushi doesn't want to hurt others. Lastly, when Fushi secludes himself on an island so that they can't use humans nearby as a way of weakening Fushi, the Nokkers then start attacking indiscriminately to bring him back out of hiding. They're the ultimate "adaptive" lifeforms and this is a trend that will continue throughout the entirety of Fushi's story.
5 They're Able To Actively Track Fushi
This next one is going to make anyone who didn't already realize this feel a bit silly, but the Nokkers are why Fushi can't ever seem to escape the Guardian Force or their Hayase-incarnation leaders. Remember, the Nokkers can seemingly track Fushi to any location, given enough time.
Fushi himself breaks it down into a 3-day system once he starts traveling the world after Jananda island, saying that they're very likely to start showing up from the 3rd day onward anywhere he stays too long. And, this is exactly how all the different Hayase descendants find Fushi, thanks to their own Nokker that's been passed down throughout their familial line.
4 They Think, Communicate, & Actively Learn
For a large part of To Your Eternity, the Nokkers are seen and described as these seemingly hive-minded or pure autonomous lifeforms with a singular goal in mind. But, as time goes on and the Nokkers become a more prevalent existence throughout the world, this thought process is re-evaluated.
After they start communicating with Fushi through people they've inhabited, such as the Guardian Force leaders, it becomes clear that Nokkers have independent thought and can even individualize themselves, as seen when Hayase's Nokker makes a deal with her and even "betrays" its own kind for Fushi. Not only that, but they can also communicate directly with their host through writing or even telepathy in certain circumstances.
3 They Have The Ability To Co-Exist
Again, as seen through Hayase's Nokker, it's clear that these things don't need to kill in order to live. This isn't some "eat to live" relationship with humanity. For one, they don't seem to actually "need" any sort of sustenance to survive. And, even when they do invade a human host, they don't have to kill it and can instead control a region of their body instead.
A good comparable example is something like Migi in Parasyte who originally wanted to take over Shinichi completely but learned to cohabitate when he was related to just Shinichi's hand. Like in Parasyte, the Nokker can basically choose to only "take over" a part of the host's body and then use their abilities through that part to give the limb or body part extra functions. This is most often seen with Kahaku, even though he uses it (most of the time) to be way too overprotective of Fushi.
2 Their Ultimate "Goal" Is Actually Rather Altruistic
Disclaimer: From here on out the Nokker facts will include heavy spoilers from where the manga is in the story and not the anime.
Now that information about the Nokkers in the manga is being used, it's time to talk about what the actual "end goal" for the Nokkers is. Basically, like the Yanome Tribe seen at the beginning of the series, the Nokkers believe that releasing the soul or "fye" from the body gives that soul true freedom and happiness.
Because of this, apparently, the Nokkers aim to free all of humanity by destroying their "vessels" and allowing their souls to be free.
1 Are They From Space Or From Paradise?
And lastly, it's still not entirely clear where Nokkers originally come from. Some fans believe them to be constructs made by some alien race to combat the Beholder and his plans on Earth. Others believe that they're souls from the afterlife who are reformed into Nokkers by some third party to come and "save" humans from their mortal peril.
But, regardless, it's now proven thanks to the modern-era events in the manga that this core belief of "death brings true freedom" isn't something all Nokkers wholly believe in. In the modern day, Nokkers are microscopic in size and actively "infect" other humans but will then make their own decision to kill their host and take them over or simply co-exist with them. It's not a "good guys win" or even a "bad guys win" scenario, they've just adapted to their situation. Funnily enough, they're like humans in the sense that broad generalizations don't work for them anymore, as some are good, some are evil, and some are in between.